This invention relates to a heating apparatus which comprises a burner, a combustion chamber, means for obtaining the mixing of a primary fluid with the combustion gases, and means for containing a secondary fluid and for allowing after the mixing of the primary fluid with the combustion gases, a heat exchange between said primary fluid and the secondary fluid to be heated.
To minimize the very large exchange surface areas which are required in the conventional heating apparatus, various apparatus have been designed for directly heating water, which allow for the same heating power of the burner, to substantially lower the magnitude of said exchange areas. However, the combustion chambers which are partly cooled by the flowing of an inner or outer water film, thus have walls which are subjected to very high temperatures, which are impossible to cool efficiently, thus causing distortions, corrodings, scale-forming cracks and finally breaking-down of said walls. There results therefrom heavy maintenance costs and a relatively short life duration of the heating apparatus, even when use is made of noble materials for the manufacture thereof.